1. Field of the Invention
The present invention relates to a disk-like information recording medium and an information recording/reproducing apparatus or an information reproducing apparatus using the disk-like information recording medium, such as a magnetic disk drive or a magneto-optical disk drive. The invention also relates to a method for establishing synchronization in the above information recording/reproducing apparatus or in the above information recording apparatus.
2. Description of the Related Art
Hitherto, in compact magnetic disk drives or magneto-optical disk drives, servo areas and user data areas are alternately and independently formed on a recording surface of a disk-like information recording medium. On the servo area, servo information required for positioning recording/reproducing means, such as a magnetic head or an optical pickup, is recorded. The methods for positioning recording/reproducing means, for example, a magnetic head, based on the servo information, include a sector servo method and a synchronous servo method.
The sector servo method is employed when the individual servo information items are asynchronous with each other. In this method, a servo clock is generated based on a reference signal (preamble) recorded on each servo area, or is generated by means such as a PLL from a data string read from each servo information item.
In contrast, the synchronous servo method is used when the individual servo information items are synchronous with each other. In this method, a servo clock is generated from clock marks which have been formed by magnetic means or physical means in predetermined areas, for example, servo areas, discretely provided on a recording surface of a disk-like information recording medium.
A synchronous servo-type magnetic disk drive will be taken by way of example in order to explain the configuration of a servo area, the initial synchronizing method, the data format, and the recording/reproducing operation, all of which are used in a known technique.
A reference will first be made to the configuration of a conventional servo area. An example of a magnetic disk used in a conventional synchronous servo-type magnetic disk drive is shown in FIG. 16. Tracks are concentrically formed on a recording surface of a magnetic disk 200. Several hundreds of servo areas and data areas are alternately and independently provided on each track at an equal pitch. Moreover, since the servo areas and the data areas are radially located on the disk, they form a sector-like region having a predetermined center angle as viewed from the overall recording surface of the disk. A combination of a servo area and an adjacent data area is referred to as a "segment" in the track direction.
Several hundreds of servo areas provided on each track, as noted above, are each formed of an address region 202, a fine region 203, and a clock region 204. Accordingly, several hundreds of address regions 202, fine regions 203, and clock regions 204 are also provided on each track.
Most of the address regions 202 are each provided with an access pattern (track address code) 205. Part of the address regions 202 are each provided with a unique pattern 208. Further, a home index pattern 209 is provided for one address region 202 on each track. The fine region 203 is provided with a fine pattern 206, while the clock region 204 is provided with a clock mark 207.
The above-described patterns and marks are as follows. The access pattern 205 is formed by coding a track address using, for example, the Gray code. The length and the position of the coded pattern are different from the other Gray code patterns on different tracks. The access pattern 205, which is used for positioning the magnetic head, is specifically required for shifting the magnetic head to a targeted track in the track/seek mode.
The fine pattern 206, which indicates the relative position of the magnetic head to the targeted track, is needed for accurately positioning the magnetic head to the center of the targeted track in the tracking mode. The fine pattern 206 is formed of four magnetic patterns, A, B, X and Y.
The clock mark 207 is used for generating clock information. More specifically, a data clock and a servo clock are generated by predetermined clock-generating means based on an isolated waveform reproduced from the clock mark 207. Although in this example the clock mark 207 is configured in a radially and continuously extended shape, various other shapes may be used.
The unique pattern 208 serves to recognize the rough position of the clock mark 207 during the initial synchronizing operation, which will be described in greater detail later. The unique pattern 208 is formed of a plurality of radially and continuously extended lines (patterns), and is easily detected even before the clock is generated. A violation code, which cannot possibly be included in a coded data string, is used to form the unique pattern 208.
The home index pattern 209 represents the rotational angle origin of the magnetic disk 200, which will be described below. The home index pattern 209 is configured in such a manner that it can be easily differentiated from the other patterns provided on a recording surface.
An explanation will now be given of an example of the initial synchronizing methods employed in a synchronous servo-type magnetic disk drive using the magnetic disk 200. It is necessary to detect the rough position of the clock mark 207 prior to an initial synchronizing operation. Thus, the foregoing unique pattern 208 is used as an auxiliary pattern. The unique pattern 208 is provided in the address region 202 where the access pattern 205 is not disposed, i.e., a unique pattern 208 is provided at fixed intervals on a track, for example, for each of several dozens of address regions 202 on each track.
Thus, in order to achieve initial synchronization, the unique pattern 208 is first detected, and after a lapse of a predetermined period measured by predetermined means, such as a clock generated by a quartz oscillator, a clock gate signal is generated to detect an isolated waveform reproduced from the clock mark 207. Based on the isolated waveform, a servo clock and a data clock are generated, thereby establishing initial synchronization.
After achieving initial synchronization, the above-described home index pattern 209 is detected and, upon detection of the home index pattern 209, the number of segments over which the magnetic head has passed is counted. Based on the number of segments, the tracking position (the position over which the magnetic head 24 floats) is recognized, thereby achieving segment synchronization, i.e., frame synchronization. Namely, the home index pattern 209 is used for recognizing the rotational angle origin.
Since one home index pattern 209 is provided on each track, a latency time of a maximum of one track revolution time is required to search the home index pattern 209. Accordingly, the same amount of time is needed for achieving frame synchronization, i.e., segment synchronization, before entering the recording/reproducing mode.
The data format used in a known magnetic disk drive is as follows. User data is recorded on or reproduced from a data area in a unit, which is referred to as a "sector" having, for example, 512 bytes. Before recording the user data, a sector identification code (hereinafter referred to as a "sector ID") and an error correcting code (hereinafter referred to as an "ECC") are added to the user data. Recorded on the sector ID are data-sector definition information and flag information representing defective sectors, together with a cyclic redundancy code (hereinafter referred to as a "CRC").
A segment, which is formed of a data area and a servo area, as noted above, represents a physical partition of a disk-like information recording medium. In contrast, a frame represents a logical partition corresponding to the information recorded on a segment. To record or reproduce the segment user data on or from a disk-like information recording medium, the logical data unit is used. Accordingly, the partitions of segments and the partitions of sectors do not necessarily coincide with each other, as illustrated in FIG. 17. Namely, the start points and the end points of the sectors are placed somewhere within the segments. In order to precisely perform a recording/reproducing operation, a hard disk controller is required to recognize in which data area of which segment the start point and the end point of a sector are placed. Thus, the information indicating the start point and the end point of a sector is recorded on the foregoing sector ID.
A method for recording user data without adding a sector ID is available. This method is referred to as "the IDless recording method". In the IDless recording method, the above-described data format is not used, and instead, the sector ID information is stored in means, such as a semiconductor memory, rather than being recorded on a disk. It is thus possible to make a small region, accounting for several per cents of the overall data area, available for the user data area, which should otherwise be spared.
The operation of an example of conventional magnetic disk drives using the IDless recording method will now be described with reference to FIG. 18. In FIG. 18, the elements corresponding to those of an embodiment of the present invention (explained later) shown in FIG. 4 are designated with like reference numerals. The conventional magnetic disk drive shown in FIG. 18 has a hard disk controller (hereinafter referred to as "the HDC") 12, a microprocessor (hereinafter referred to as "the MPU") 11 for controlling the operation of the magnetic disk drive, and a conventional random access memory (hereinafter referred to as "the buffer RAM") 13. The HDC 12 is loaded with various functions, such as an interface function for connecting the magnetic disk drive to a host computer, a data recording/reproducing control function, and a processing function which performs predetermined operations, such as adding an ECC based on recording/reproducing data. The random access memory 13 is provided to compensate for a difference in the data transfer rate between the host computer and the magnetic disk drive. Further, a timing generating circuit 16 generates, based on a clock signal supplied from a clock generating circuit 115, various timing signals required for recording/reproducing operations.
The HDC 12 is provided with a frame counter which counts, based on a segment (frame) signal supplied from the timing generating circuit 16, the number of frames over which a magnetic head 24 passes. Considering all the factors, such as the number of frames, the frame number set by the MPU 11 according to the recording/reproducing command, and the sector head signal supplied from the timing generating circuit 16, the position of the magnetic head 24 on a recording surface of the magnetic disk 200 is recognized by the HDC 12. Namely, by counting the number of segments from the rotational angle origin and the number of bytes by using the frame counter and the byte counter, respectively, the HDC 12 is always able to recognize the position of the magnetic head 24 on the magnetic disk 200.
Prior to the recording/reproducing operation, for example, when power is supplied to the magnetic disk drive, a sector ID information table is created in predetermined storage means, such as the buffer RAM 13, in the form of firmware of the MPU 11.
As noted above, the start point or the end point of a sector is placed, as shown in FIG. 17, somewhere within a segment on the magnetic disk 200. Accordingly, since servo areas interrupt a sector, it is necessary that the recording/reproducing operation is skipped during a period in which the magnetic head 24 passes over the servo area. The skip information required for controlling the recording/reproducing operation in the above manner and another type of information, such as defective and unusable sectors, are recorded in the sector ID information table.
FIG. 19 illustrates an example of the sector ID information table. Sector shown in this table indicates the sector number. Since one or a plurality of servo areas interrupt each sector, as noted above, each sector is divided into two or more sector fragments partitioned by the servo areas. The information concerning the sector fragments is indicated by SkipFlag, LastFlag, and Count. Sector fragments having SkipFlag "1" are unusable due to defects. Sector fragments having LastFlag "1" are finished halfway through a data area before reaching a subsequent servo area.
Count represents the number of bytes from the head to the end of a sector fragment. Count of a sector fragment having LastFlag "0" indicates the number of bytes from the head of the sector fragment to the servo-area starting point. Count of a sector fragment having LastFlag "1" indicates the number of bytes from the head of the sector fragment to the end of the sector to which the sector fragment belongs. Thus, the following operation is required for the sector fragments having LastFlag "0". When the number of bytes recorded on Count is reached after the data recording/reproducing operation is started, the data recording/reproducing operation is suspended to wait for the magnetic head 24 to pass over the servo area.
This will be explained in greater detail with reference to FIG. 20 in the case where the data recording/reproducing operation is performed on, for example, sector 1 shown in FIG. 19. The head of sector 1 is first recognized from a sector head signal supplied from the timing generating circuit 16. Since LastFlag of the sector fragment of sector 1 corresponding to the first line of the table shown in FIG. 19 indicates "0", "0200" shown in Count represents the number of bytes from the head of the first sector fragment of sector 1 to the starting point of the servo area. Accordingly, when "0200" is counted, the magnetic head 24 reaches the starting point of the servo area. It is thus necessary to suspend the data recording/reproducing operation and then to restart the operation after the magnetic head 24 passes over the servo area.
Processing is then executed on the second fragment of sector 1 shown in FIG. 19. Access is started from the head of the data area of the subsequent segment, and the number of bytes from the head to the end of the data area is counted in a manner similar to the first sector fragment. LastFlag of the second sector fragment of sector 1 indicates "1", the end point of the sector is located somewhere within the same data area. Accordingly, Count of "1FFF" in the table shown in FIG. 19 represents the number of bytes from the head of the second sector fragment of the sector 1, i.e., the head of the data area in the subsequent segment, to the end of sector 1 located somewhere within the same data area. When the HDC 12 counts up the total number of bytes including 512 bytes of a sector and bytes forming the ECC, the end of the sector can be recognized.
As discussed above, frame synchronization is achieved based on the unique pattern 208 and the home index pattern 209, and the sector ID table is created. In this state, the following recording/reproducing operation is ready to be performed. Upon receiving from the host computer an instruction to perform a recording or reproducing operation on a sector, the MPU 11 sets the start frame number, the start sector number, the end frame number, and the end sector number in various registers of the HDC 12. Then, the following operation is started based on the above numbers set in the registers.
Referring back to FIG. 18, a seek/tracking operation is first performed on the start track by a positioning control circuit 17. Upon completion of the seek/tracking operation, a disk sequencer of the HDC 12 is actuated. Every time a segment signal is received from the timing generating circuit 16, the frame counter counts up. After it is determined by referring to the count number of the frame counter that the foregoing start frame number set in the register of the HDC 12 is reached, a sector head pulse is fed from the timing generating circuit 16 to cause the sector counter to count up. Similarly, after it is recognized by referring to the sector ID information table that the targeted sector is reached, a recording/reproducing operation is initiated. Thereafter, the recording/reproducing operation continues while referring to the sector ID information table.
The following problems are encountered by the foregoing conventional disk-like information recording mediums and information recording/reproducing apparatuses using such disk-like information recording mediums. After synchronization is established relative to the clock mark based on the unique pattern, a latency time equal to a maximum of one track revolution time is required for detecting the home index pattern in order to achieve frame synchronization. This lengthy latency time is seriously critical particularly for switching recording surfaces. Namely, in a disk-like information recording medium having double recordable and reproducible surfaces, the transfer rate is seriously reduced from the normal transfer rate while the recording surfaces are switched.
In order to overcome the above drawback, when the home index pattern is recorded or formed on the address region, the rotational positions of double surfaces of the recording medium must be highly accurately aligned with each other. This eliminates the need for changing the frame counter number even after the recording surfaces are switched. It is also necessary to produce a highly precise recording/reproducing magnetic head corresponding to each recording surface. The above requirements, however, greatly increase the complexity of the manufacturing processes of the disk-like information recording medium and the magnetic head.
The above-described problem is noticeable both in the synchronous servo-type magnetic disk drive and the sector servo-type magnetic disk drive. Particularly in the synchronous servo-type magnetic disk drive, since there are many servo samples, the physical pitch between servo areas becomes extremely small, thereby decreasing a margin in the manufacturing process for the disk-like information recording medium. Consequently, in order to ensure a sufficient level of reliability of an information recording medium, every time recording surfaces are switched, the home index pattern should always be detected so as to recognize the rotational position from the rotational angle origin.
The foregoing IDless recording method in which the data efficiency is improved also presents a problem concerning the reliability of the data recording operation. If the IDless recording method is not employed, i.e., if a sector ID is added to the user data of each sector, the recording operation is started by reading the sector ID recorded on the disk-like information recording medium. Thus, the possibility of performing a recording operation at an incorrect position is very small.
According to the IDless recording method, however, if a frame pulse or a sector pulse fails to be input into the HDC for some reason, the HDC counter is erroneously operated to perform a recording operation at an incorrect position. What is worse, once such a recording operation is started at an incorrect position, there is no measure to immediately stop the operation. More specifically, once a recording operation is started at an incorrect position, the recording operation is continuously performed on the areas over which the magnetic head passes until the magnetic head reaches the rotational angle origin to reset the frame counter. This may even destroy recorded data.
The foregoing problem is presented both in the synchronous servo method and in the sector servo method.